The present invention relates to a natural stone element in the form of a large-format plate for lining facades of buildings.
It is known to divide natural stone, in particular marble, into plate-shaped portions and to use these stone plates for lining facedes or inside walls of buildings.
Such plates are generally attached to the building with the aid of cliplike mounting elements. These clips are connected in an appropriate way with the supporting structure of the building, on the one hand, and hold the stone plate at their edges in the selected position, on the other hand. The clips engage recesses provided for this purpose on the edges of the plates.
The technical requirements for such a facade lining depend on this static edge mounting and the expected wind forces, as well as on the combined effect of dimensions, thickness and weight. They also determine the costs for material and attachment. When very solid natural stone such as marble is used as a facade lining, it does not allow for a wall thickness smaller than 30 mm due to its material structure and its material properties as well as the above-mentioned edge mounting. Since dimensions and wall thickness determine weight, the use of large-format stone plates for facades reaches a technical and financial limit at dimension of approximately 500.times.1500 mm. This limit becomes more acute the higher the building and the wind load stressing.
For these cases, as well as for applications involving normal requirements, solutions have been proposed for saving weight by joining stone plates with reduced wall thicknesses to thin-walled lightweight supporting plates made of other materials, such as aluminum, platics or the like.
The use of aluminum for forming supporting plates has the advantage that the stone plates, that are basically brittle and very breakable under load, in particular in large formats, are combined with a flexurally strong material that can be used in small wall thicknesses, saves weight and can readily be joined with the stone plate to form a composite plate system. An aluminum plate also provides a great number of possibilities for attaching the large-size plate to the building that are appropriate for the material involved, so that one is free of the disadvantages of edge mounting for natural stone mainly due to the brittleness and lack of flexural strength of this material.
In the case of larger formats, in particular as of one square meter, and use for facades, however, there is a risk of detachment and breakage of the stone plate.
The applicant has found that these disadvantages are mainly due to the fact that the metal supporting plate, when heated, expands much more than the stone plate. The use of shear-resistant adhesives for connecting the aluminum plate to the stone plate allows for some compensation of this difference in expansion, but with larger plates and greater alternating temperature stresses as occur for facades, no lasting success can be achieved with such adhesives, so that this type of composite plate has a limited lifetime.
In the ceramic field, composite tiles are already known (DE-OS 27 45 250) which are intended to reduce the occurrence of temperature expansion stresses and possibly resulting cracks in that the materials of the composite element have approximately the same coefficient of temperature expansion and the adhesive connecting the plate elements has elastic properties. However, in this case the plate forming the visible surface is made of ceramic material and the carrier plate is made of acrylic concrete. To increase the plate stability, one has further suggested providing the back of the acrylic concrete carrier plate with reinforcement ribs running over the edge of the plate and extending obliquely across the back of the plate.